Area 51 is the unofficial name for the United States test and training facility. Until July 2013, its existence was denied, that all changed when the C.I.A., the Central Intelligence Agency officially acknowledged its existence. Ref: NY Times
The site is easily viewable on both Bing and Google map views. In Google Earth, you can walk round a 3D Visualisation of the base without being picked up any security guards. The buildings are based on overheard shots and photos from a distance. The below has come from Bing maps. It has been a source of theorists including conspiracy theorists who believe that the base is where the Government is keeping dead aliens and space ships. It is believed that all the waste from the plant is buried on site somewhere so that it can't be exhumed by people wanting to know more including foreign intelligence spies.
The site was first set up to help the C.I.A. to develop spy planes, ones that would fly higher than normal planes so that would not be shot down. One spy plane flown by Gary Powers was once shot down over USSR. The pilot was captured, tried and put in prison and eventually released on a prisoner swap. Other inventions to have probably had development time at the site is the B-2 Stealth Bomber.
Area 51, is located in Southern Nevada, not far from Las Vegas, the gambling capital of the world. It is a highly guarded by the military with orders to shoot to protect the secrets but probably never do unless for warning shots, On signs round the base, it does warn legal force is authorized. Patrols are ongoing round the site in 4x4 with the guards warning people off the site.
Although it has only been officially recognised by the C.I.A., its been an open secret, the Russians would almost certainly have known about the location long before the American public knew about the existence.
In 1995, Independence Day, the film featured the location heavily and those who weren't aware of the location certainly did so by then. In the movie, an alien craft was being stored at the location only to be reactivated when the aliens return. When the producers of the film wanted the US Air Force to help them make the movie, the USAF was all too happy to help out in the production of the film as they were seen as the heroes. When the USAF heard Area 51 would be featured in the film, the co-operation abruptly ended unless references to the area were removed, they weren't and the USAF withdrew.
People have reported seeing strange lights in the sky over Groom Lake doing things that no ordinary aircraft could possibly do. There have been many books written on the subject and one person is suing the US Government over his health after working at the installation. In 1989, Bob Lazar went on television to tell people of the existence of what was at the secretive location but he was soon discredited. 2.
Employees are brought to the site by plane from Las Vegas airport on a secure flight.